Transfer switches for tap-changing regulating transformers having squirrel-cage-shaped support for the fixed contacts thereof



Nov. 16, 1965 A. BLEIBTREU 3, 0

TRANSFER SWITCHES FOR TAP-CHANGING REGULATING TRANSFORMERS HAVING SQUIRREIr-CAGE-SHAPED SUPPQRT FOR THE FIXED CONTACTS THEREOF Filed June 21, 1963 s Sheets-Sheet 1 Mme-Mm? WWW QMMM Nov. 16, 1965 A. BLEIBTREU 3,218,400

TRANSFER SWITCHES FOR TAP-CHANGING REGULATING TRANSFORMERS HAVING SQUIRREL-CAGE-SHAPED SUPPORT FOR THE FIXED CONTACTS THEREOF Filed June 21, 1963 3 Sheets-Sheet 2 MII/IIIIE illillll fl n J MM Q 9: K

WM M NAM W UM 6, 1965 A. BLEIBTREU 3,218,400

TRANSFER SWITCHES FOR TAP-CHANGING REGULATING TRANSFORMERS HAVING SQUIRREL- E-SHAPED SUPPORT FOR THE FIXED TACTS THEREOF 3 Sheets-Sheet 5 Filed June 21, 1965 Imam/r0? mm @Mm United States Patent 3,218,400 TRANSFER SWITCHES FOR TAP-CHANGING REG- ULATING TRANSFORMERS HAVING SQUIR- REL-CAGE-SHAPED SUPPORT FOR THE FIXED CONTACTS THEREOF Alexander lBleibtreu, Regensburg, Germany, assignor to Maschinenfabrik Reinhauscn Gehruder Scheubeck K.G., Regensburg, Germany Filed June 21, 1963, Ser. No. 289,517 Claims priority, application Germany, July 21, 1962, M 53,648 12 Claims. (Cl. 200-8) This invention is concerned with transfer switches for tap-changing regulating transformers.

It is a general object of this invention to provide improved transfer switches for tap-changing regulating transformer.

It is another object of this invention to provide improved transfer switches of the type wherein each circuit opening operation comprises the formation of two serially related points of break, which points of break have a significant spatial separation, thus resulting in a reduction of the recovery voltage per break and minimizing the danger of contamination of some points of break by products of arcing formed at other points of break.

Another object of this invention is to provide transfer switches which can be more readily maintained than comparable prior art transfer switches.

Another object of this invention is to provide transfer switches having longer creepage path and a higher dielectric strength than comparable prior art transfer switches.

Another object of this invention is to provide improved transfer switches for so-called Janson type tap-changing regulating transformers.

Another object of this invention is to provide an improved version of the transfer switch disclosed and claimed in the copending patent application of Alexander Bleibtreu, filed Jan. 31, 1963, Ser. No. 255,291 for Transfer Switch for Tap Changers for Regulating Transformers.

Tap-changing regulating transformers include selector switches and transfer switches. The selector switches serve the purpose of selecting a particular tap on a tapped transformer winding intended to be connected into an electric circuit. Selector switches are not required to interrupt current carrying circuits, or to close on current carrying circuits. This tas k is performed by the transfer switches. The latter perform all switching operations under load. Therefore all arcing is kept away from the selector switches and occurs only at the transfer switches. It is, therefore, of considerable importance that the transfer switches be designed to effectively cope with power arcs resulting from load switching operations and overload switching operations.

The above and additional objects and advantages of the invention will become more apparent from the ensuing description thereof when read in connection with the accompanying drawings wherein:

FIG. 1 shows a prior art transfer switch know as pennant transfer switch;

FIG. 2 is mainly a vertical section through a transfer switch for a three phase circuit embodying the present invention, some parts thereof being shown in front elevation rather than in vertical section;

FIG. 3 is a horizontal section through the structure of FIG. 2 showing the fixed main contacts and the fixed auxiliary contacts of three phases thereof in top-plan view and showing movable main contacts and the movable auxiliary contacts of but one of the three phases;

FIG. 4 is an isometric view of a portion of the structure of FIGS. 2 and 3.

3,218,400 Patented Nov. 16, 1965 The aforementioned term pennant transfer switch has been coined by Bernhard Janson to whom the development of this type of transfer switches is due.

FIG. 1 shows a portion Tr of a tapped transformer Winding. The transfer switch comprises four movable contacts 1, 2, 3, 4. A cylindrical contact support 6a of insulating material supports four fixed contacts adapted to be cooperatively engaged by the aforementioned movable contacts 1, 2, 3, 4. The taps U U of the tapped portion of winding Tr are directly connected by appropriate leads to the outer or fixed main contacts of the transfer switch. The taps U U are further connected by the intermediary of ohmic resistors R to the inner or fixed auxiliary contacts of the transfer switch. The movable contacts 1 and 3, on the one hand, and the movable contacts 2 and 4, on the other hand, form part of separate or different contact operating systems. This makes it possi ble to adjust the operating times of movable contacts 1 and 3 relative to the operating times of movable contacts 2 and 4. In the position of the contacts shown in FIG. 1 tap U is directly connected to a point indicated by a small arrow. Changing the connection of that point from tap U to tap U involves a closing operation of movable auxiliary contact 3 preceding the separation of the left movable main contact 1 from its cooperating fixed main contact. Since the fixed auxiliary contact cooperating with the movable auxiliary contact 3 is connected to tap U by the intermediary of right resistor R, the closing operation of contact 3 gives rise to a circulating current. This circulating current is superimposed upon the load current. As mentioned above, contact 1 parts subsequent to engagement by movable contact 3 of its cooperating fixed contact. Parting of contact 1 from its cooperating fixed contact is followed by engagement by contact 4 of its fixed cooperating contact and by separation of contact 2 from its fixed cooperating contact. The gist of pennant transfer switches of which FIG. 1 shows but one of many possible embodiments resides in the fact that prior to interrupting a circuit including a given tap, another pre-selected tap is being connected into the circuit by the intermediary of an ohmic resistor. As a result, the difference in potential between taps U and U gives rise to a circulating current and it is the algebraic sum of this circulating current and of a load current indicated by an arrow which must be interrupted by the pennant transfer switch. This is a relatively onerous interrupting duty. On the other hand, operation of a pennant transfer switch has little effect upon the system voltage.

In order to form two serially related breaks at each point of break rather than but one single break, a pair of fixed contacts may be substituted for each fixed contact of the structure of FIG. 1 and each movable contact of the structure of FIG. 1 may be adapted to selectively engage such a pair of fixed contacts and to part from such a pair of fixed contacts. The embodiment of the invention shown in FIGS. 2-4 is a transfer switch adapted in the aforementioned fashion to form serially related double breaks at each point of break.

The three phase transfer switch shown in FIGS. 2-4 comprises a cylindrical tank 1 accommodating the coaxial supporting structure 2. Structure 2 comprises a bottom frame member 3, a top frame member 4 and a plurality of vertically insulating rods or bars 5. The latter are angularly displaced and spaced and supported by frame members 3, 4. Thus parts 3, 4, 5 form a squirrel cage structure. Tank 1 may contain a body of dil (not shown). Terminal 1a is integral with tank 1 which may be made of an appropriate insulating material. This terminal is intended to connect the transfer switch to the neutral point of the regulating transformer. Other terminals (not shown) provide a connection between the transfer switch and the selector switch of the transformer. The latter terminals may be arranged in pairs in view of the high current-carrying duty imposed upon these parts. If tank 1 is made of a casting resin the terminals of the transfer switch may be in the form of inserts in the casting as shown in the upper left corner of FIG. 1.

Top frame member 4 is made of metal and provided with contacts cooperatively engaging with terminal 1a. A structure substantially in the shape of a second radially inner squirrel-cage is suspended on frame member 4 by means of screws 11. The above mentioned second structure substantially in the shape of a squirrel-cage comprises the upper plate member 12, the lower plate member 13 and three conductive vertical bars 14 extending parallel to the common axis of tank 1 and first squirrel-cage structure 3, 4, 5. Bars 14 enclose angles of 360/3=l20 degrees. The upper end plate 15 and the lower end plate 16 are fixedly mounted upon operating shaft 17 resting in bearings 17a, 17b. Shaft 17 is arranged in coaxial relation to tank 1 and squirrel cage structures 2 and 12, 13, 14, respectively. Rods 18 of which but one is shown in the drawings are spaced from shaft 17 and extend parallel to shaft 17. The upper ends and the lower ends of rods 18 are loosely guided by the upper end plate 15 and the lower end plate 16, respectively. The upper ends of rods 18 are mechanically tied to the upper end plate 15 by means of helical tension springs 19 of which but one is shown in the drawings. In like fashion the lower ends of rods 18 are mechanically tied to the lower end plate 16 by means of helical tension springs 19 of which but one has been shown in the drawings. Reference numeral 20 has been applied to indicate a plurality of upper contact operating arms and reference numeral 21 has been applied to indicate a plurality of lower contact operating arms. Each contact operating arm 20, 21 has a radially inner bearing 18a and a radially outer bearing 22a. Rods 18 extend through the radially inner bearings 18a of contact operating arms 20, 21. The bearings 22a on the radially outer ends of each pair of contact operating arms 20, 21 support a vertical shaft 22 which, in turn, supports a contact carrier 23. Contact carriers 23 insulatingly support contact bridges 24 extending parallel to operating shaft 17. Reference numeral 24a has been applied in FIG. 2 to indicate the insulating layer separating each contact carrier 23 from the contact bridge 24 being carried by it. The aforementioned upper and lower plate members 12, 13 are provided with radially extending slots or grooves 12' and 13, respectively, engaged by and guiding the upper and the lower ends of contact carriers 23. Because of this function of plate members 12, 13 the same may be referred to as guide plates.

The upper end of each contact bridge 24 and the lower end of each contact bridge 24 are adapted to cooperate with a pair of fixed contacts 6, 6. Each pair of fixed contacts 6 is supported by one of the aforementioned vertical bars forming part of squirrel cage structure 2. Bars 5 are made of an appropriate insulating material and are preferably H-shaped in cross-section. Thus each bar 5 defines a radially inner channel-shaped space and a radially outer channel-shaped space. Contacts 6 are accommodated in the radially inner channel-shaped spaces defined by bars 5. Contacts 6 are maintained in position on bars 5 by means of screws or equivalent defined by rods or bars 5. Therefore the heads 25 of the screws are located in the radially outer channel spaces defined by rods ro bars 5. Therefore the heads 25 of the screws supporting fixed contacts 6 are readily accessible from the outside of radially outer cage structure 2.

The circuitry of FIG. 1 calls for the provision of four contact carriers 23 and of four contact bridges 24 and of four pairs of fixed contacts 6, 6 per phase. In other applications the number of contact carriers, contact bridges and of pairs of fixed contacts per phase may be smaller than four or larger than four. Thus the structure of FIGS. 2-4 comprises six pairs of fixed contacts 6, 6 and six movable contact bridges 24 per phase. As shown in FIG. 3 the contacts 6, 6, 24 of each phase are arranged in form of a sector of a circle. The fixed contacts 6, 6 at the ends of each such sector are main arcing contacts and the fixed contacts of each such sector arranged between main contacts are auxiliary arcing contacts to be connected to switching resistors such as the resistors R shown in FIG. 1. FIG. 3 shows all the arcing contacts pertaining to one phase, omitting the movable arcing contacts or contact bridges 24 of the two other phases.

The current path of the structure of FIGS. 2-4 is substantially the same as explained in connection with FIG. 1. The current path extends through lower arcing contacts 6, contact bridges 24 and upper arcing contacts 6. Upper contacts 6 are conductively connected to element 4 which is, in turn, connected to the neutral point of the three phase system. (The conductor means conductively connecting the upper contacts 6 to element 4 and thus establishing a Y connection have been omitted in FIG. 2.)

The kinematic theory underlying the structure of FIGS. 2 to 4 is set forth in detail in United States Patent 2,680,- 790 to Bernhard Jansen, June 8, 1954 for Load Changeover Switch for Tapped Transformers Using a Combination of Contact Movements (see particularly FIG. 5 and column 6, line 55 to column 7, line 23) and reference may be had to that patent for additional information regarding this subject. The operation of the structure of FIGS. 2-4 is briefly as follows: Pivotal movement of shaft 17 under the bias of the spring of a switch operating mechanism (not shown) results in rotary motions of parts 15, 16 transmitted to shafts 18. The pivotal motion of shaft 18 about the vertical axis of the switch causes movement of contact carriers 23 relative to plates 12, 13, the upper and lower ends of contact carriers 23 sliding in grooves 12', 13' of guide plates 12, 13. As a result contact bridges 24 are moved radially either into engagement with fixed contacts 6, 6, or out of engagement with fixed contacts 6, 6.

It will be apparent from the foregoing that transfer switches embodying the present invention dispense entirely with flexible connections, or braids, for energizing the movable contact segments including contact bridges 24.

Since contact bridges 24 are insulated from their supports 23, all the movable parts within the transfer switch may be made of metal rather than of insulating material, which greatly contributes to the ruggedness of transfer switches embodying the present invention. The ruggedness of such transfer switches is due in particular to the presence of the squirrel-cage type structure comprising guide plates 12, 13 and the three conductive squirrel-cage bars 14.

Though the double break feature embodied in the structure of FIGS. 2-4 greatly increases the life of the cooperating contacts 6, 24, 6, it is of great importance to readily obtain access to all parts of the switch which are subjected to wear and tear. Heretofore the inspection and/or replacement of the radially outer fixed contacts was a relatively difiicult task, requiring a radially inward retraction of the contact bridges and their supporting structures. Performance of this task calls for special tools and highly skilled labor. The structure of FIGS. 2-4 greatly facilitates inspection and/ or replacement of fixed contacts 6, 6. All that is required to this end is removal of the contact supporting bars 5 from cage structure 2. This can be readily achieved since the heads 25 of the bar-supporting screws are arranged on the radially outer surfaces of bars 5. The gaps which are present between contiguous bars 5 make it possible to inspect the transfer switch in a general way upon removal thereof from its oil-filled tank 1 without disassembly of any parts thereof. Since the contacts 6, 6 and their supporting rods or bars 5 are surrounded by oil or other equivalent insulating liquid on all the sides thereof, creepage paths otherwise always present in the fixed contact supporting structure of transfer switches are substantially eliminated, resulting in a considerable increase of the dielectric strength of the structure. Another factor tending to increase the dielectric strength of the structure is the arrangement of contacts 6, 6 within recesses or channels formed by rods 5. Replacement of a pair of defective fixed contacts can readily be achieved by removing its contact supporting rod and replacing the same by a like rod having contacts in perfect operating condition.

The entire transfer switch structure inside of insulating housing 1 may be lifted bodily out of the latter for the purpose of inspection, maintenance and repair. When the transfer switch has been lifted out of tank 1 its fixed contacts 6 and its contact bridges 24 are substantially exposed to view through the gaps formed between contiguous contact supports 5. This greatly facilitates inspection of the fixed contacts and the contact bridges. Replacement of any pair of fixed contacts which may show evidence of excessive wear or erosion may be readily effected by substituting a new contact support 5 with a pair of new fixed contacts 6 thereon for the contact support with the contacts showing evidence of excessive wear or erosion. A body of oil, or other insulating fiuid, filled into tank 1 envelops each of the contact supporting bars 5 from all sides thereof, i.e. there is liquid around each contact supporting bar 5 in any direction at right angles to each contact-supporting bar 5. Thus creepage paths between fixed contacts 6 being at different potentials are completely avoided in the present structure. Such creepage paths are a serious limitation of all transfer switches having fixed contacts supported by an insulating cylinder on the inside thereof rather than by a system of spaced rods forming a squirrelcage-like structure of which each bar is surrounded on all sides thereof by a body of insulating liquid.

Although I have shown and described a specific structure, it is to be clearly understood that the same was merely for the purpose of illustration, and that changes and modifications may readily be made by those skilled in the art without departing from the spirit and scope of the invention.

I claim as my invention:

1. A transfer switch for tap-changing regulating transformers comprising in combination:

(a) a tank including a cylindrical lateral wall;

(b) a plurality of pairs of superimposed registering fixed contacts inside said tank arranged relatively close to said lateral wall thereof but spaced from said lateral wall to establish a gap of predetermined width between each of said plurality of pairs of contacts and said lateral wall;

(c) a plurality of movable, contact bridges inside said tank arranged more remotely from said wall thereof than said plurality of pairs of fixed contacts, each of said plurality of contact bridges being adapted to cooperate with one of said plurality of pairs of contacts; (d) operating means for operating said plurality of contact bridges to sequentially engage and part from one of said plurality of pairs of fixed contacts; and

(e) a plurality of spaced rod-like insulating members fixedly supported inside of said tank extending parallel to and spaced from said lateral wall of said tank, each of said plurality of members supporting one of said plurality of pairs of fixed contacts.

2. A transfer switch for tap-changing regulating transformers as specified in claim 1 wherein each of said plurality of spaced members defines on the radially inner side thereof a channel space accommodating one of said plurality of superimposed registering pairs of fixed contacts.

3. A transfer switch for top-changing regulating transformers as specified in claim 1 wherein each of said plurality of members is substantially H-shaped in crossseetion, each defining a radially outer channel-shaped space and a radially inner channel-shaped space separated by a web, each radially inner channel-shaped space of said plurality of members accommodating one of said plurality of pairs of fixed contacts, and wherein fastener means securing one of said plurality of pairs of fixed contacts to each of said plurality of members are arranged in each radially outer channel-shaped space of each of said plurality of members.

4. A transfer switch for tap-changing regulating transformers as specified in claim 1 comprising a body of insulating liquid in said tank filling the spaces between contiguous members and Wholly surrounding each of said members of said plurality of members.

5. A transfer switch for tap-changing regulating transformers comprising in combination:

(a) a tank including a lateral Wall in the shape of a cylindrical surface;

(b) a plurality of pairs of fixed contacts inside said tank arranged relatively close to said lateral wall thereof, and equidistantly spaced therefrom, each pair of said plurality of pairs of fixed contacts being aligned along a straight line parallel to the axis of said cylindrical surface;

(c) a plurality of movable contact bridges inside said tank arranged more remotely from said lateral wall thereof than said plurality of pairs of fixed contacts;

(d) operating means for moving said plurality of contact bridges sequentially selectively radially inwardly and radially outwardly to cause said plurality of contact bridges to part from and to engage said plurality of pairs of fixed contacts;

(e) an insulating support for said plurality of pairs of fixed contacts formed by a structure substantially in the shape of a squirrel-cage and including a bottom frame member, a top frame member and a plurality of angularly spaced supporting bars for said plurality of fixed contacts extending between said bottom frame member and said top frame member and supported by said bottom frame member and by said top frame member, said plurality of supporting bars being spaced radially from said cylindrical surface of said tank and each of said plurality of supporting bars defining jointly with said cylindrical surface of said tank a gap of predetermined width, and each of said plurality of supporting bars supporting on the radially inner side thereof one of said plurality of pairs of fixed contacts.

6. A transfer switch as specified in claim 5 wherein said plurality of supporting bars are secured to said bottom frame member and to said top frame member by fastener means accessible from the radially outer surfaces of said plurality of supporting bars.

7. A transfer switch for tap-changing regulating transformers comprising in combination:

(a) a plurality of pairs of spaced fixed contacts, said plurality of pairs of contacts including two outer pairs of fixed main contacts and inner pairs of auxiliary fixed contacts arranged between said two pairs of fixed main contacts;

(b) a plurality of contact bridges each adapted to cooperate with one of said plurality of pairs of fixed contacts, said plurality of contact bridges including two main contact bridges each adapted to cooperate with one of said two pairs of fixed main contacts, and said plurality of contact bridges further including auxiliary contact bridges each adapted to cooperate with one of said pairs of auxiliary fixed contacts;

(c) operating means for moving said plurality of contact bridges sequentially selectively radially inwardly and radially outwardly to cause said plurality of contact bridges to part from and to engage said plurality of pairs of fixed contacts;

(d) a plurality of angularly spaced insulating rods arranged in a cylindrical surface and forming a squirrel-cage structure, each of said plurality of insulating rods supporting one of said plurality of pairs of fixed contacts on a side thereof juxtaposed to one of said plurality of contact bridges; and

(e) a body of insulating liquid surrounding each of said plurality of insulating rods on all the sides thereof.

8. A transfer switch for tap-changers for regulating transformers comprising in combination:

(a) a cylindrical switch housing;

(b) a plurality of pairs of fixed contacts inside said housing, each pair of said plurality of pairs of fixed contacts being arranged along a line parallel to said switch housing, and each of said plurality of pairs of fixed contacts being angularly spaced from a contiguous pair of said plurality of pairs of fixed contacts;

(0) a plurality of movable contact bridges arranged inside of said housing, extending in a direction longitudinally thereof each adapted to cooperate with one of said plurality of fixed contacts;

(d) a plurality of contact carriers each supporting one of said plurality of contact bridges;

(e) means for electrically insulating each of said plurality of contact bridges from the contact carrier thereof;

(f) a pair of spaced fixed guide plates defining grooves at juxtaposed sides thereof engaged by the upper end and by the lower end of each of said plurality of contact carriers;

(g) a plurality of angularly spaced conductive bars extending in a direction longitudinally of said housing for spacing said pair of guide plates;

(h) pivotable operating means including linkage means for causing radial movement of said plurality of contact carriers relative to said pair of guide plates to effect a predetermined sequential engagement of each of said plurality of pairs of fixed contacts by one of said plurality of contact bridges, and

(i) a plurality of angularly spaced insulating rods arranged substantially in a cylindrical surface coaxial to said switch housing and forming a cage structure radially spaced from said cylindrical switch housing, each of said plurality of insulating rods supporting one of said plurality of pairs of fixed contacts on the side thereof juxtaposed to said plurality of contact bridges.

9. A transfer switch for tap-changers for regulating transformers comprising in combination:

(a) a cylindrical housing;

(b) a plurality of pairs of fixed contacts inside said housing, each pair of said plurality of pairs of fixed contacts being aligned along a line parallel to said switch housing and each of said plurality of pairs of fixed contacts being angularly spaced from a contiguous pair of said plurality of pairs of fixed contacts;

(c) a plurality of movable contact bridges arranged inside said housing, extending in a direction longitudinally thereof and adapted to sequentially cooperate with one of said plurality of pairs of fixed contacts;

(d) a plurality of contact carriers each insulatingly supporting one of said plurality of contact bridges;

(e) an upper fixed guide plate defining groove means engaged by the upper end of each of said plurality of contact carriers;

(f) a lower fixed guide plate defining groove means engaged by the lower end of each of said plurality of contact carriers;

(g) an operating shaft for operating said plurality of contact bridges and for operating said plurality of contact carriers arranged inside said housing in coaxial relation thereto;

(h) a pair of spaced end plates fixedly mounted on said shaft for joint operation with said shaft;

(i) rod means arranged parallel to said shaft in spaced relation therefrom having ends supported by said pair of end plates;

(j) a plurality of pairs of contact operating arms, each of said plurality of pairs of contact operating arms having radially inner bearings mounted on said rod means and having radially outer bearings;

(k) a plurality of shafts arranged parallel to said rod means in spaced relation therefrom each pivotally securing one of said plurality of contact carriers to one of said radially outer bearings of one of said plurality of pairs of contact operating arms; and

(l) a plurality of angularly spaced insulating rods forming a cage structure coaxial to and radially spaced from said cylindrical housing, each of said plurality of rods supporting one of said plurality of pairs of fixed contacts and each of said plurality of rods defining a channel on the radially inner side thereof wherein one of said plurality of pairs of fixed contacts is recessed.

it). A transfer switch for tap-changing regulating transformers comprising in combination:

(a) a cylindrical housing;

(b) a plurality of pairs of spaced fixed arcing contacts inside said housing, each of said plurality of pairs of fixed arcing contacts being arranged along one of a plurality of angularly displaced generatrices of a cylindrical surface parallel to and spaced from said housing, said plurality of pairs of fixed arcing contacts including two outer pairs of fixed main arcing contacts and inner pairs of fixed auxiliary arcing contacts arranged between said two pairs of main arcing contacts;

(0) a plurality of parallel contact bridges arranged inside said housing, extending in a direction longitudinally thereof and each being adapted to engage with, and part from, one of said plurality of pairs of fixed arcing contacts, said plurality of contacts bridges including two main contact bridges each adapted to engage with, and to part from, one of said two pairs of fixed main arcing contacts, and said plurality of contact bridges further including auxiliary contact bridges each adapted to engage with, and to part from, one of said pairs of fixed auxiliary arcing contacts;

((1) operating means for said plurality of contact bridges to cause in a predetermined sequence engagement of each of said plurality of contact bridges with, and parting of each said plurality of contact bridges from, one of said plurality of pairs of spaced fixed arcing contacts, said operating means including a driving shaft arranged in said housing in coaxial relation thereto, a pair of spaced end plates fixedly mounted on and jointly pivotable with said shaft and a plurality of linkage means for transmitting the pivotal motion of said pair of end plates to said plurality of contact bridges; and

(e) a plurality of angularly spaced insulating bars arranged substantially in said cylindrical surface and forming a cylindrical cage structure coaxial to and radially spaced from said cylindrical housing, each of said plurality of bars being substantially H-shaped in cross-section and defining a radially inner channel and a radially outer channel, each of said plurality of bars supporting one of said plurality of pairs of fixed arcing contacts recessed in said radially inner channel thereof.

11. A transfer switch for tap-changing regulating transformers comprising in combination:

(a) a cylindrical housing;

(b) a plurality of pairs of spaced fixed arcing contacts inside said housing, each of said plurality of pairs of fixed arcing contacts being arranged along a line parallel to said cylindrical housing;

() a plurality of contact bridges arranged inside said housing, extending in a direction longitudinally thereof and each being adapted to engage with, and to part from, one of said plurality of pairs of fixed arcing contacts;

(d) a pair of grooved spaced guide plates for guiding the upper ends and the lower ends of said plurality of contact bridges;

(e) a plurality of conductive bars extending parallel to said plurality of contact bridges and conductively interconnecting said pair of guide plates and jointly forming with said pair of guide plates a first squirrelcage-like supporting structure for said plurality of contact bridges;

(f) operating means for said plurality of contact bridges to cause engagement of each of said plurality of contact bridges with, and parting of each of said plurality of contact bridges from, one of said plurality of pairs of fixed arcing contacts in a predetermined sequence, said operating means including a driving shaft arranged in said housing in coaxial relation thereto, a pair of axially spaced end plates having a larger axial spacing than the axial spacing of said pair of guide plates and fixedly mounted on and jointly pivotable With said shaft and a plurality of linkage means for transmitting the pivotal motion of said pair of end plates to said plurality of contact bridges;

(g) means for electrically insulating said plurality of contact bridges from said first squirrel-cage-like supporting structure and from said plurality of linkage means; and

(h) a plurality of angularly spaced insulating bars arranged substantially in a cylindrical surface coaxial to and radially spaced from said cylindrical housing, each of said plurality of bars supporting at a side thereof juxtaposed to one of said plurality of contact bridges one of said plurality of pairs of fixed arcing contacts.

12. A transfer switch for tap-changing regulating transformers comprising in combination:

(a) a cylindrical switch housing;

(b) a plurality of pairs of spaced fixed arcing contacts inside said housing, each of said plurality of pairs of fixed arcing contacts being arranged along one of a plurality of lines parallel to said housing;

(c) a plurality of contact bridges arranged in said housing extending in a direction longitudinally thereof and each being adapted to engage with, and to part from, one of said plurality of pairs of fixed arcing contacts;

(d) a plurality of contact bridge supports each for one of said plurality of contact bridges, each of said plurality of supports having an upper guiding extension and a lower guiding extension;

(e) electric insulating means insulating each of said plurality of contact bridges from the contact bridge support thereof;

(f) a pair of axially spaced guide plates defining grooves at the juxtaposed surfaces thereof engaged by said upper guiding extension and by said lower guiding extension of said plurality of contact bridge supports for guiding the upper ends and the lower ends of said plurality of contact bridge supports;

(g) a plurality of conductive bars extending parallel to said plurality of contact bridges conductively interconnecting said pair of guide plates and jointly forming with said pair of guide plates a first squirrelcage-like supporting structure for said plurality of contact bridges and said plurality of contact bridge supports;

(h) operating means for said plurality of contact bridges and for said plurality of contact bridge supports to cause engagement of each of said plurality of contact bridges with, and parting of each of said plurality of contact bridges from, one of said plurality of pairs of fixed arcing contacts in a predetermined sequence, said operating means including a driving shaft arranged in said switch housing in coaxial relation thereto, a pair of axially spaced end plates having a larger axial spacing than the axial spacing of said pair of guide plates and fixedly mounted on and jointly pivotable with said shaft and a plurality of linkage means for transmitting the pivotal motion of said pair of end plates to said plurality of contact bridge supports;

(i)a plurality of angularly spaced insulating bars arranged substantially in said cylindrical surface and forming a second squirrel-cage-like supporting structure coaxial to and radially spaced from said cylindrical switch housing and supporting said plurality of fixed arcing contacts; and

(j) a plurality of screws for securing said plurality of bars to fixed surfaces situated adjacent the ends of said plurality of bars, said screws having screw heads arranged at the radially outer surfaces of said plurality of bars.

References Cited by the Examiner UNITED STATES PATENTS 6/1954 Jensen. 5/1958 Jensen.

FOREIGN PATENTS 5/1959 Italy. 

1. A TRANSFER SWITCH FOR TAP-CHANGING REGULATING TRANSFORMERS COMPRISING IN COMBINATION: (A) A TANK INCLUDING A CYLINDRICAL LATERAL WALL; (B) A PLURALITY OF PAIRS OF SUPERIMPOSED REGISTERING FIXED CONTACTS INSIDE SAID TANK ARRANGED RELATIVELY CLOSE TO SAID LATERAL WALL THEREOF BUT SPACED FROM SAID LATERAL WALL TO ESTABLISH A GAP OF PREDETERMINED WIDTH BETWEEN EACH OF SAID PLURALITY OF PAIRS OF CONTACTS AND SAID LATERAL WALL; (C) A PLURALITY OF MOVABLE, CONTACT BRIDGES INSIDE SAID TANK ARRANGED MORE REMOTELY FROM SAID WALL THEREOF THAN SAID PLURALITY OF PAIRS OF FIXED CONTACTS, EACH OF SAID PLURALITY OF CONTACT BRIDGES BEING ADAPTED TO COOPERATE WITH ONE OF SAID PLURALITY OF PAIRS OF CONTACTS; (D) OPERATING MEANS FOR OPERATING SAID PLURALITY OF CONTACT BRIDGES TO SEQUENTIALLY ENGAGE AND PART FROM ONE OF SAID PLURALITY OF PAIRS OF FIXED CONTACTS; AND (E) A PLURALITY OF SPACED ROD-LIKE INSULATING MEMBERS FIXEDLY SUPPORTED INSIDE OF SAID TANK EXTENDING PARALLEL TO AND SPACED FROM SAID LATERAL WALL OF SAID TANK, EACH OF SAID PLURALITY OF MEMBERS SUPPORTING ONE OF SAID PLURALITY OF PAIRS OF FIXED CONTACTS. 